Why dont you turn the multiplayer version of stalker into MMO create a bigger zone in wich players can join stalker clans and play a cooperative game to explore the zone make the zone bigger with so called dungeons that takes a lot of ppl to explore etc.
SImple multiplayer game with about 32 to 64 players locked in a small map with no options to moove out of it dosent trigger the hype level anymore thats why Masive Multiplayer games like battleground europe Lineage and World of warcraft make a lot of money and make games like battlefield call of duty and counter-strike look dull.
So far there is nothing unique in the stalker multiplayer however its seen that the game looks really cool expecially with the added weather effects and night and day change there is a future for stalker it can easly be as profitable as world of warcraft if constructed right !
Also singleplayer is a lot of fun but hey most ppl go for online games these days because in online games you never know whats gonna happen while singleplayer offline games you hardly play more than once unless the game is really cool with posibilty to explore

I voted "Yes"
But
Call of Duty 2 is still fun (even CoD 1 is)
Playing on a server in a complete 20 km² zone will require servermaintance and overpopulation will kill the atmosphere.
A Stalker-Dungeon ? Like 40 people exploring a big underground base and searching for epic gear? ; D And doing it over and over again...
Stalker is a game were you have to be alone or in a small group to save the reality - an army of 40 stalkers will overrun every enemy (like the military base) and the magic will be gone...
I like RPG and I like FPS and I like endless fields. A MMORPGFPS would be grate. Like endless (realistic) war or something. But we have to live with what we have. ^^

Toxins, pollutants and poisonous gasses
Without notice take their toll on the masses
Air becomes thicker than the water we drink
People unaware of the spread of disease
Smoke fills the sky and the sun disappears
Rain from above is like acid filled tears

---QUOTATION---Playing on a server in a complete 20 km² zone will require servermaintance and overpopulation will kill the atmosphere.
A Stalker-Dungeon ? Like 40 people exploring a big underground base and searching for epic gear? ; D And doing it over and over again...
Stalker is a game were you have to be alone or in a small group to save the reality - an army of 40 stalkers will overrun every enemy (like the military base) and the magic will be gone...---END QUOTATION---

That was exactly my point...I'd rather the dev's put time and money into a concept that not only works, but is in high demand. Like co-op. I just don't see a way that they could actually make another game that is an MMO with this story line. It'd destroy the very reason that makes the game great. It's why the Sim's Online never really "took off" like Will Wright (the creator of the Sims) wanted to. It became a flashy chat room instead of a world you can create and alter. Stalker would be destroyed for the exact same reason if made into an MMO.
The game would be better served with maybe a special co-op add-on. In the add-on would be a lobby room so that you could meet people and collect groups of people to go adventuring with in the SP game. It makes more sense to do it that way than a conventional MMO with hundreds running around messing up the atmosphere. And, isn't that essentially what an MMO is? A chat room where you talk to people looking for people, places, and things. Then you go on adventures with them? It'd just be better handled really that way rather than a whole new MMO Stalker game.

Actually they can make the idea going if they fit it into the concept of ever changing zone . The zone can change evolve and expand they even can update it to winter time
ALso the stalkers still can be in small squad nobody said it has to be set to 40 ppl its mearlly an idea can be oriented towards pvp and exploring and rival faction wars they can even put vehicles to make it more intresting.
As for COD2 game is awsome however they did very small maps in multiplayer and didnt give the players the ability to drive vehicles id rather play united offensive!

Here is what can work few stalker factions fighting for the controll of the zone with theritorry that can be captured wich generate income for buying equipment vehicles to gear the faction stalkers there coulld be also places hard to explore and require teamwork but with good rewards.

---QUOTATION---MMOs are stupid and degenerating to gameplay. I hate to imagine what Stalker would be like with people sitting around farming for loot and exp.---END QUOTATION---

so there IS a need for new-type based MMOs
like no xp or something
no skill points (i should i specc my stalker on survival, aiming or beast mastery? xD or better on assassination, combat and subtiety...)
imagine a world (a huge one) with stalker gameplay - it has not to be the zone...just maybe a battlefield or a fictive country

Toxins, pollutants and poisonous gasses
Without notice take their toll on the masses
Air becomes thicker than the water we drink
People unaware of the spread of disease
Smoke fills the sky and the sun disappears
Rain from above is like acid filled tears